The goal of this research is to understand the nature of language deficits displayed by aphasic patients and to characterize the mechanisms responsible for them. The research focuses on on-line processing impairments. Both speech production and speech perception will be studied. The interface between speech perception and lexical access and syntactic processing also will be investigated. Speech production studies will explore whether anterior aphasic patients have impairments in the timing of two independent articulators, studying the nasal manner of articulation and the timing relation between release of oral closure and lowering the velum. To determine whether other properties of speech are spared, spectral properties of place of articulation for nasal consonants in the vicinity of nasal release, are studied. Whether aphasic patients can implement phonetic parameters of speech in larger contexts, the effects of regressive assimilation on phonetic patterns of voicing in fricative consonants will be investigated. In the speech production studies, acoustic analyses will investigate the vocal tract gestures for particular acoustic patterns. In speech perception, a new method will be used to study patients perceptions of temporal, spectral and amplitude parameters. These parameters will be studied using computer editing of natural speech or via speech synthesis, with subjects using reaction times measurements in a discrimination task. Further studies will investigate the extent to which acoustic/ phonetic variants of a phonetic category affect word recognition. An auditory repetition priming paradigm will be used, as well as a lexical decision paradigm. Finally, using lexical decision tasks, the investigators will conduct a series of on-line experiments to assess whether aphasic individuals assign the correct antecedent to an anaphor.